Electron lens for convergence of plurality of beams

ABSTRACT

An electron lens transmitting a plurality of electron beams from a source thereof to converge at different points on a screen whereby aberrations are caused to occur thereat, and each of two electrodes included in the lens are formed with spaced elongated openings of preselected configurations and predetermined dimensions in electrode sections adjacent to spaced peripheries of the electron lens for transmitting the respective beams through the peripheral openings in the respective electrodes to converge at a common point on the screen to minimize aberrations thereat.

1 51 July 18, 1972 54 ELECTRON LENS FOR CONVERGENCE 1561 ReferencesCited OF PLURALITY 0F BEAMS UNITED STATES PATENTS [72] Inventors:Yoshlzumi Terazawa; Kazuo Ayald, both 21,96,571 12/1954 Law ..313/92 BXof Tokyo Japan 3,448,316 6/1969 Yoshida et al. ..313/69 c [73] A551 nee:Ni n Electri g T0352) Japan c Company umucd' Primary Examiner-RobertSegal Al!0rneyMam & .langarathis [22] Filed: July 23, 1970 21 Appl.No.:57,481 ABSTRACT An electron lens transmitting a plurality of electronbeams [30 F A from a source thereof to converge at different points on aoreign pp rcatlon lriorlty Dam screen whereby aberrations are caused tooccur thereat, and July 25, 1969 Japan; .j ..44/591s0 each of twoelectrodes indluded in the lens are formed i spaced elongated openingsof preselected configurations and 52 us. Cl.. ..3l3/69 R, 313/700predetermined dimensions in electrode Sections adjacent w 51 me 01 .110129 00 1101 29/50, HOlj 31/00 Spaced peripheries of the elwwn lens fortransmitting the [58] Fieldoi-Search .;...J;...;.....i.....313/6907009213 "spgcfive W the periPheral Openings the j 4 respectiveelectrodes to converge at a common point on the screen to minimizeaberrations thereat. v

4Claim,6Drawing Figures 'PATENTED JUL! 8 m2 Fig. 4.

Fig. 5.

Fig.

INVENTORS Yoshizumi Terozczwa Kazuo Ayaki mam & a/rlgywwfiiz ATTORNEYSELECTRON LENS FOR CONVERGENCE OF PLURALYI'Y OF BEAMS BACKGROUNDDESCRIPTION OF THE lNVENll ON This invention relates to an electron lensused for electron discharge devices, and more specifically to an el lensused for color television picture tubes.

In the conventional electrostatic electron lens, the further theelectron beam is away from the center axis of the electron lens, thegreater becomes the aberration. in such electron lens used in acathode-ray tube, the electron spot coming out on the fluorescent screenspreads with a considerable amount of distortion when the electron beamispassed through the outer portion of the electron lens. This resultsinloose resolution and has made the electron lens impracticable. in orderto avoid the above-mentioned difficulties, the color television. picturetube, for example, which is to require a plurality of electron beams hashitherto been provided with as many elecing with respect to its lengthdirection can be determined to a value between infinity and f,, and thatwith respect to the breath direction can be detemiined to a valuebetween f, and f whi h are p'ven by above equations (1) and ('2). Thisteaches us that the elongated opening, when used as a divergradialdirection than in the lateral direction of the lens. On the other hand,according to this invention, an excessively strong I converging effectin the radial direction of the electron lens can be compensated by arelatively strong diverging effect in the transverse direction of theelongated opening. In other words, by suitably determining thelength-breadth ratio of the tron lenses as the electron beams used, sothat each electron 2 elongated opening and thus suitably compensatingthe conbeam may pass through the center portion of each electron lens,or has been provided with one electron lens so designed that all theelectron beams may through the center portion of the electron lens orotherwise the diameters of the electron lens must increased. To realizethese, however, design difficulties have been inevitable.

The object of this invention is to provide an electrostatic electronlens, which with only little aberration, converges the electron beamspassing through its edge portion.

verging effect, it becomes possible to minimize the aberration in thelens.

F10. 1 is an optical model diagram illustrating the aberration in aconventional electron lens;

F1G.2 is an optical model diagram illustrating the principles of thepresent invention;

FlG.3 is an axial sectional diagram showing a specific em- 7 bodiment ofthe invention; and

FTGS. 4,5 and 6 are plan views of components usable in An electron lensembodying this invention has as its element FIG 3.

such an electrode as having at least one elongated opening whoselongitudinal direction is perpendicular to both the radial direction andthe center axis of the electrode, in order that the electron beam offthe center axis passes through said openings. (Note: Said perpendiculardirection will hereinafter be called lateral direction").

The elongated opening disposed in the electrode of the electron lensaccording to this invention serves as a diverging lens having arelatively strong diverging effect in the radial direction of theelectrode and a relatively weak diverging effeet in the lateraldirection, to compensate the aberration in the electron lens.

Assume that a small circular hole is disposed in a metal plate having anelectric potential of V, and an electron beam perpendicular to the metalplate passes through the hole, and that the electron beam advances inthe positive direction. Then the focal distance f, of the electron lensformed by the circular hole is expressed as:

where E, is an electric field on the side from which the electron beamenters the circular hole E, is an electric field on the side to whichthe electron beam 55 comes out of the circular hole. ,When, instead ofthe small circular hole, a straight slit is disposed therein, the focaldistance with respect to the focusing action in the longitudinaldirection of the slit is infinite.

The focal distance f with respect to the focusing action in the 0transverse direction of the slit is expressed by the following equationwhen the potential Vand electric fields E and E are the same as above.

DETAILED DESCRIPTION The invention will be explained in detail byreferringto the appended drawings.

FlG.1 illustrates an optical model of a conventional electrc lens andsome electron beams passing through the edge portion of the lens,wherein light rays 13, 14 and 15 parallel to the principal axis 12,after passing through a convex lens 11, and

cross the principal axis 12 at points 13, 14 and 15'. This takes placedue to the well-known spherical aberration and has been thoughtunavoidable in the conventional electron lens. A light beam having acircular section 16' on the plane 16 comes out to cast its cross section17', 18 and 19' on the planes 17, 18 and 19, respectively, beingrefracted through the 0 direction.

F162 is an optical model showing the principles of this invention. InFIG.2 light rays 24, 25 and 26 parallel to the principal axis 22 andincident upon the convex lens 21, respectively, are shown as an opticalmodel of electron rays passing through the edge portion of an electronlens. Also, in F162 a concave lens 23 having a stronger diverging effectin the direction parallel to the plane of the drawing than in thedirection perpendicular to the plane of the drawing is shown as anoptical model regarding the elongated opening of this invention.Relating the optical model of FIG]. the light rays 24,25 and 26 aresuitably diverged and compensated by the concave lens 23 in the radimdirection of the convex lens 21 and then are converged by the convexlens 21. As a result, the

=2 V/ E 2 li t rays 24, 25 and 26 are focused nearl at the int 28 on f:t 2 y p In other words, the focal distance of the slit is half that ofthe circular hole, and if E is larger than E in either case, then thefocal distance will be negative and the small circular hole or the thinopening will work as a diverging lens.

the principal axis 22, and a light beam having a circular section 27 onthe plane 27 comes out as a very small converged light beam having across section 28' on the plane 28.

FlG.3 is to illustrate the first embodiment of this invention.

The elongated opening becomes nearly circular or to be In FlG.3 anelectron beam from the triode part consisting of a able to be consideredas a circular hole, as the value of the length-breadth ratio of theelongated opening approaches l. While, the elongated opening becomes aslit as the lengthbreadth ratio increases. Hence, by suitably selectingthe cathode electrode 301, a first grid electrode 302 and a second gridelectrode 303 is moderately converged by a prefocus lens part formedbetween the second grid electrode 303 and third grid electrode 304.Then, the electron beam, after passing length-breadth ratio, the focaldistance of the elongated openthrough the elongated opening 305 disposedin the third grid lens type, and a positive high voltage is applied tothc third grid electrode 304 and fifth grid electrode 307, while, hfourth grid electrode 306 is held at nearly zero potential. When theforward direction-of the electron beam 3l0 is assumed positive, theelectric field strength on h l ft f h elongated opening 305 of the thirdgrid electrode 304 is negative and relatively small and that on theright is positive and relatively large. Therefore, the elongated opening305 operates as a diverging lens. The electric field on the left of theelongated opening 308 disposed in the fifth grid electrode 307 isnegative and relatively large, and that on the right is nearly zero.Therefore-the elongated opening 308 operates also as a diverging lens.in F162 one diverging lens is used for compensation purpose. While, intheembodiment as in FlG.3, the both elongated openings 305 and 308 areused and have a diverging effect for compensation so that even strongaberration may be compensated. Accordingly, the main lens part mayoperate with little aberrationand good converging efiect on .theelectron .beam 3.10passing through the. edgeportion. of the main lens.As a result, the electron beam 310 comes out as a sufficiently smallelectron spot on the fluorescent screen 309. In FIG. 3, only oneelectron beam 310 is shown. Practically, however, three electron beamshaving circular sections (the lateral section of these electron beamsare positioned at the vertex of an equilateral triangle) are used in thecolor television picture tube and, therefore, three pairs of elongatedopenings 305 and 308 must be provided.

FIG. 4 shows an arrangement of three elongated openings. These openings42 are disposed so that their longitudinal directions are coincidentwith the lateral direction of the elec trode 41. It is necessary tosuitably determine the lengthbreadth ratio of the elongated opening 42for effective aberration compensation. It is also necessary todetermine. the breadth (the narrower one of the distances across theopening) to be wide enough to pass the electron beam.

FlG.S shows the third and fifth grid electrodes of the second embodimentof the invention. These electrodes 51 are provided with are shapedelongated openings 52 which are disposed along the circumference of theelectrodes.

These arc-shaped elongated openings have nearly the same aberrationcompensating effect as the straight elongated opening. The arrangementin FlGS is characterized in that there will be little deviation in thepositional relationship between the electron beam and the elongatedopening even if a small amount of error is caused in the lateraldirection in the electrode assembly process.

F K]. 6 is to illustrate the third embodiment of the invention, whereineach of the third and fifth grid electrodes 61 is provided with acircular hole 62 in the center, and also with areshaped elongatedopenings 63 disposed on the outer side of the circular hole 62. Thisembodiment is an example applied to the color television picture tube ofso-called inline type in which the lateral sections of three electronbeams are aligned at equal intervals on one straight line. According tothis embodiment, the hole in the center is circular because the centerelectron beam passes through the center of the electron lens to causelittle aberration and no compensation on aberration is needed.

In the foregoing embodiments, the unipotential lens is employed.Instead, other types oflenses, for example, bipotential lens, may beused for aberration compensation according to this invention.

While a few embodiments of the invention have been described, it isparticularly understood that invention is not limited thereto orthereby.

What is claimed is:

l. A cathode-ray tube comprising in combination:

means producing a plurality of electron beams,

a screen receivin said beams; a plurality of hol ow electrodes separatedby an open ended cylindrical electrode and spaced in tandem between saidbeam means and screen whereby said screen and electrodes are providedwith acommon center axis; said electrodes energized with electricpotentials of predetermined magnitudes for transmitting said beamstherethrough on further axes spaced from said center axis to incidencewith said center axis at points off said screen to cause an aberrationof said beams at said screen; and

means compensating for said aberration, including first and second ofsaid electrodes provided with mutually opposing closed ends disposedperpendicularly to and coaxial with said center axis, each of said endsformed with elon gated openings equal in number to the number of saidbeams, each opening receiving a corresponding beam, and spaced from saidcenter axis and provided with a preselected configuration, said openingshaying preassigned maximum and minimum dimensions of which said minimumdimension is disposed in a radial direction relative to said center axisfor transmitting all electrons of said respective beams said openingsaligned in one plane for transmitting said respective beams to move saidpoints to incidence with said center axis at said screen to compensatefor said aberration. I

2. The cathode-ray tube according to claim 1 in which said openings havepreselected rectilinear configurations.

3. The cathode-ray tube according to claim 1 in which said openings havepreselected curvilinear configurations.

4. A cathode-ray tube comprising in combination:

a screen receiving a plurality of electron beams;

means producing said plurality of electron beams of which a central onehas an axis coincident with a center axis of said screen,

a plurality of hollow electrodes separated by an open ended cylindricalelectrode and spaced in tandem between said beam means and screenwhereby said electrodes are provided with an axis coincident with saidone beam and screen axis; said electrodes energized with electricpotentials of predetermined magnitudes for transmitting another of saidbeams through said electrodes on a further axis spaced from saidelectrode axis to incidence with said screen axis at a first point offsaid screen to cause an aberration ofsaid another beam; and

means compensating for said aberration, including first and second ofsaid electrodes provided with mutually oppos ing closed ends disposedperpendicularly to and coaxially with said electrode axis; each of saidends formed with a central opening coaxial with said screen, one beamand electrode coincident axes for transmitting all electrons of saidcentral one beam andwith at least one elongated opening spaced from saidelectrode axis and having maximum and minimum dimensions of which saidminimum dimension is disposed in a radial direction relative to saidelectrode axis for transmitting all electrons of said another beam; saidelongated openings aligned in one plane for transmitting said anotherbeam to move said first incident point to coincidence with said screenaxis at said screen to compensate for said aberration.

1. A cathode-ray tube comprising in combination: means producing aplurality of electron beams, a screen receiving said beams; a pluralityof hollow electrodes separated by an open ended cylindrical electrodeand spaced in tandem between said beam means and screen whereby saidscreen and electrodes are provided with a common center axis; saidelectrodes energized with electric potentials of predeterminedmagnitudes for transmitting said beams therethrough on further axesspaced from said center axis to incidence with said center axis atpoints off said screen to cause an aberration of said beams at saidscreen; and means compensating for said aberration, including first andsecond of said electrodes provided with mutually opposing closed endsdisposed perpendicularly to and coaxial with said center axis, each ofsaid ends formed with elongated openings equal in number to the numberof said beams, each opening receiving a corresponding beam, and spacedfrom said center axis and provided with a preselected configuration,said openings having preassigned maximum and minimum dimensions of whichsaid minimum dimension is disposed in a radial direction relative tosaid center axis for transmitting all electrons of said respective beamssaid openings aligned in one plane for transmitting said respectivebeams to move said points to incidence with said center axis at saidscreen to compensate for said aberration.
 2. The cathode-ray tubeaccording to claim 1 in which said openings have preselected rectilinearconfigurations.
 3. The cathode-ray tube according to claim 1 in whichsaid openings have preselected curvilinear configurations.
 4. Acathode-ray tube comprising in combination: a screen receiving aplurality of electron beams; means producing said plurality of electronbeams of which a central one has an axis coincident with a center axisof said screen, a plurality of hollow electrodes separated by an openended cylindrical electrode and spaced in tandem between said beam meansand screen whereby said electrodes are provided with an axis coincidentwith said one beam and screen axis; said electrodes energized withelectric potentials of predetermined magnitudes for transmitting anotherof said beams through said electrodes on a further axis spaced from saidelectrode axis to incidence with said screen axis at a first point offsaid screen to cause an aberration of said another beam; and meanscompensating for said aberration, including first and second of saidelectrodes provided with mutually opposing closed ends disposedperpendicularly to and coaxially with said electrode axis; each of saidends formed with a central opening coaxial with said screen, one beamand electrode coincident axes for transmItting all electrons of saidcentral one beam and with at least one elongated opening spaced fromsaid electrode axis and having maximum and minimum dimensions of whichsaid minimum dimension is disposed in a radial direction relative tosaid electrode axis for transmitting all electrons of said another beam;said elongated openings aligned in one plane for transmitting saidanother beam to move said first incident point to coincidence with saidscreen axis at said screen to compensate for said aberration.